Poor finish, aluminium

emtor said:
The problem is I don't have a clue at what temps aluminium should be subjected to in order to heat treat it.
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You can heat treat it. Surprised it's hard for you to find, especially in the age of Google. Heat treating data for Al is in the same places you would expect to find heat treating data for steels.
the answer is here (NIST heat treating pdf)
 
I suspect the aluminium may also be sticking to the surface of the tool. That will cause problems. Try keeping the tool 'wet' with light oil or WD40 or even just kero (for aluminium). NOT NOT flood coolant! Just a drop or two now and then.

I was using a 1 mm ball end cutter to scribe a fiducial on some 6060 plate. The groove was rough with ??melted?? residues. I switched the pulsed mister on and ... a beautiful finish. For misting I use 3 parts kero to 1 part (cheapest) olive oil.

And for aluminium, you need really sharp tools meant for aluminium. Do NOT try using them on steel as well: that will kill the sharp edge.

Cheers
Roger
 
For now I only have the carbide inserts that came with the lathe, but HSS blanks are on the way in the mail.
 
I don’t think I e ever gotten a mirrored finish on my cast aluminum. It does matter what your melting for sure. I melt a lot of engine parts or parts that have already been cast before. Degassing makes a big deal with pinholes.
The insert looks like a neg. insert. Which is dull for cutting aluminum. You would have a lot cheaper tool pressure to get a cut. Then probably dragging from the pressure. In my experience you want a sharp tool a little lube and you should get pretty good results.
 
Cadillac said:
I don’t think I e ever gotten a mirrored finish on my cast aluminum. It does matter what your melting for sure. I melt a lot of engine parts or parts that have already been cast before. Degassing makes a big deal with pinholes.
The insert looks like a neg. insert. Which is dull for cutting aluminum. You would have a lot cheaper tool pressure to get a cut. Then probably dragging from the pressure. In my experience you want a sharp tool a little lube and you should get pretty good results.
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The large wheel had nearly zero pinholes. Later I poured smaller chunks that has plenty.

As for the strange finish where it varied between mirror to torn up on the same pass I think I found the cause.
The compound rest is bolted to the cross slide (T-slots) with two bolts. Loosening these bolts allows you to adjust the angle by turning the compound.
Fastening the bolts presses a disk down to the cross slide and thereby locks it down.
I noticed, when doing facing cuts, that the face got convex, and at first I suspected the carriage was moving so I locked it down.
I turned out it was the compound that gave way when applying pressure to the cutting tool.
Today I drilled two extra holes in the base, so now it's secured by four bolts, which helped. Compound rest is rock steady now, and my next lathe will be a hog of a lathe weighing more than my car :)
 
emtor said:
I turned out it was the compound that gave way when applying pressure to the cutting tool.
Today I drilled two extra holes in the base, so now it's secured by four bolts, which helped. Compound rest is rock steady now, and my next lathe will be a hog of a lathe weighing more than my car :)
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In the mean time, something like this might be a good option to tighten it up.

https://www.hobby-machinist.com/threads/1127-solid-tool-post-mount.73336/

It made a big difference on my little lathe.
 
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